io_uring/rsrc: store folio shift and mask into imu

Store the folio shift and folio mask into imu struct and use it in
iov_iter adjust, as we will have non PAGE_SIZE'd chunks if a
multi-hugepage buffer get coalesced.

Signed-off-by: Chenliang Li <cliang01.li@samsung.com>
Reviewed-by: Anuj Gupta <anuj20.g@samsung.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/20240731090133.4106-2-cliang01.li@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Chenliang Li

io_uring/rsrc.c

@@ -915,6 +915,8 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 	imu->ubuf = (unsigned long) iov->iov_base;
 	imu->ubuf_end = imu->ubuf + iov->iov_len;
 	imu->nr_bvecs = nr_pages;
+	imu->folio_shift = PAGE_SHIFT;
+	imu->folio_mask = PAGE_MASK;
 	*pimu = imu;
 	ret = 0;
 
@@ -1031,23 +1033,18 @@ int io_import_fixed(int ddir, struct iov_iter *iter,
 		 * we know that:
 		 *
 		 * 1) it's a BVEC iter, we set it up
-		 * 2) all bvecs are PAGE_SIZE in size, except potentially the
+		 * 2) all bvecs are the same in size, except potentially the
 		 *    first and last bvec
 		 *
 		 * So just find our index, and adjust the iterator afterwards.
 		 * If the offset is within the first bvec (or the whole first
 		 * bvec, just use iov_iter_advance(). This makes it easier
 		 * since we can just skip the first segment, which may not
-		 * be PAGE_SIZE aligned.
+		 * be folio_size aligned.
 		 */
 		const struct bio_vec *bvec = imu->bvec;
 
 		if (offset < bvec->bv_len) {
-			/*
-			 * Note, huge pages buffers consists of one large
-			 * bvec entry and should always go this way. The other
-			 * branch doesn't expect non PAGE_SIZE'd chunks.
-			 */
 			iter->bvec = bvec;
 			iter->count -= offset;
 			iter->iov_offset = offset;
@@ -1056,12 +1053,12 @@ int io_import_fixed(int ddir, struct iov_iter *iter,
 
 			/* skip first vec */
 			offset -= bvec->bv_len;
-			seg_skip = 1 + (offset >> PAGE_SHIFT);
+			seg_skip = 1 + (offset >> imu->folio_shift);
 
 			iter->bvec = bvec + seg_skip;
 			iter->nr_segs -= seg_skip;
 			iter->count -= bvec->bv_len + offset;
-			iter->iov_offset = offset & ~PAGE_MASK;
+			iter->iov_offset = offset & ~imu->folio_mask;
 		}
 	}
 

io_uring/rsrc.h

@@ -46,7 +46,9 @@ struct io_mapped_ubuf {
 	u64		ubuf;
 	u64		ubuf_end;
 	unsigned int	nr_bvecs;
+	unsigned int    folio_shift;
 	unsigned long	acct_pages;
+	unsigned long   folio_mask;
 	struct bio_vec	bvec[] __counted_by(nr_bvecs);
 };